The following disclosure relates to image producing machines, and more particularly to solid ink machines that use a phase change ink melting and control apparatus.
In general, phase change ink image producing machines, such as printers, employ phase change inks that are in the solid phase at ambient temperature, but exist in the molten or melted liquid phase (and can be ejected as drops or jets) at the elevated operating temperature of the machine or printer. At such an elevated operating temperature, droplets or jets of the molten or liquid phase change ink are ejected from a printhead device of the printer onto a printing media. Such ejection can be directly onto a final image receiving substrate, or indirectly onto an imaging member before transfer from it to the final image receiving media. In any case, when the ink droplets contact the surface of the printing media, they quickly solidify to create an image in the form of a predetermined pattern of solidified ink drops.
An example of such a phase change ink image producing machine or printer, and the process for producing images therewith onto image receiving sheets is disclosed in U.S. Pat. No. 6,905,201, issued on Jun. 14, 2005, to Leighton et al., the disclosure of which is incorporated herein by reference. As disclosed therein, a high-speed phase change ink image producing machine, such as printer 10 shown in FIG. 1, includes a frame 11 to which are mounted directly or indirectly all its operating subsystems and components. One of the components is an imaging member 12 that is shown in the form of a drum, but can equally be in the form of a supported endless belt. The imaging member 12 has an imaging surface 14 that is movable in the direction 16, and on which phase change ink images are formed.
The high-speed solid ink printer 10 also includes a phase change ink system 20 that has at least one source 22 of a single color phase change ink in solid form. When the printer 10 is a multicolor image producing machine, the ink system 20 includes four sources 22, 24, 26, 28, representing four different colors CYMK (cyan, yellow, magenta, black) of phase change ink solid pieces, as shown in FIG. 1. The phase change ink system 20 also includes a solid phase change ink melting and control assembly or apparatus 100 (FIG. 2) for melting or phase changing the solid form of the phase change ink into a liquid form, and for then supplying the liquid form towards the printhead system 30. The printhead system 30 includes at least one printhead assembly 32, or in the case of a high-speed, or high throughput, multicolor image producing machine, four separate printhead assemblies 32, 32, 36 and 38, as shown in FIG. 2.
The solid ink image producing printer 10 further includes a substrate supply and handling system, which may, for example, include multiple substrate supply sources 42, 44, 46, 48. The substrate supply and handling system further includes a substrate treatment system 50 that has a substrate pre-heater 52, substrate and image heater 52, and a fusing device 60. The phase change ink image producing printer 10 as shown may also include an original document feeder 70 that has a document holding tray 72, document sheet feeding and retrieval devices 72, and a document exposure and scanning system 76.
Operation and control of the various subsystems, components and functions of the machine or printer 10 are performed with the aid of a controller or electronic subsystem (ESS) 80. The ESS or controller 80 for example is a self-contained, dedicated mini-computer having a central processor unit (CPU) 82, electronic storage 82, and a display or user interface (UT) 86. The ESS or controller 80 for example includes sensor input and control means 88 as well as a pixel placement and control means 89. In addition the CPU 82 reads, captures, prepares and manages the image data flow between image input sources such as the scanning system 76, or an online or a work station connection 90, and the printhead assemblies 32, 32, 36, 38. As such, the ESS or controller 80 is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the machine's printing operations.
In operation, image data for an image to be produced is sent to the controller 80 from either the scanning system 76 or via the online or work station connection 90 for processing and output to the printhead assemblies 32, 32, 36, 38. Additionally, the controller determines and/or accepts related subsystem and component controls, for example from operator inputs via the user interface 86, and accordingly executes such controls. As a result, appropriate color solid forms of phase change ink are melted and delivered to the printhead assemblies. Additionally, pixel placement control is exercised relative to the imaging surface 12 thus forming desired images per such image data, and receiving substrates are supplied by anyone of the sources 22, 22, 26, 28 and handled by means 50 in timed registration with image formation on the surface 12. Finally, the image is transferred within the transfer nip 92, from the surface 12 onto the receiving substrate for subsequent fusing at fusing device 60.
Thus an exemplary high-speed phase change ink image producing machine 10 includes: (a) a control subsystem 80 for controlling operation of all subsystems and components thereof, (b) a movable imaging member 12 having an imaging surface 14; (c) a printhead system 30 connected to the control subsystem 80 for ejecting drops of melted molten liquid ink onto the imaging surface 12 to form an image; and (d) a phase change ink system 20 connected to the printhead system 30.
In one embodiment, the phase change ink system 20 includes a solid phase change ink melting and control apparatus 100 (FIG. 2), including a pre-melter assembly 200 and a melter assembly 300. The pre-melter assembly 200 is suitable for controllably supplying solid pieces of phase change ink from the sources 22, 22, 26, 28 to the melter assembly 300 located below the pre-melter assembly 200, and more particularly to the separate melters 300A-D. A melted molten liquid ink storage and control assembly 400 is located below the melter assembly 300. The phase change ink melting and control apparatus 100 is thus suitable for melting solid phase change ink into melted molten liquid ink, and for controlling the melted molten liquid ink.
In high throughput solid ink systems, the storage and control assembly 400 may incorporate a dual reservoir system, as illustrated in FIG. 3, corresponding to each of the individual melters 300A-D for the various colors implemented in the solid in system. In this system, molten liquid ink is fed from a corresponding melter 300A-D into an associated primary reservoir 402, which stores a first volume of melted ink for subsequent use. This reservoir is connected by a conduit or passageway 406 to a secondary reservoir 404, which stores a second volume of melted liquid ink. The liquid ink is ejected from the secondary reservoir at outlet 410 and typically through a heated routing system to reach a respective printhead or printheads of the printhead assembly 30. In systems of this type, pressurized air P is provided at port 412 to act on the free surface of the liquid ink in the secondary reservoir to discharge ink into the outlet 410. The volume of ink in the primary reservoir 402 is typically maintained at atmospheric pressure.
As shown in FIG. 3, the level of the two volumes of ink in the primary and the secondary reservoirs 402, 404 is the same under equilibrium conditions. It can be appreciated that after liquid ink has been dispensed under pressure through the outlet 410, the ink level in the secondary reservoir will drop, as depicted in FIG. 3. Once the pressurized air at port 412 ceases, the pressure above the surface of the second volume of ink in the secondary reservoir returns to atmospheric. However, due to the difference in ink height, a fluid pressure differential results between the two reservoirs. This pressure differential causes molten ink to flow from the primary reservoir 402, through the passageway 406 and into the secondary reservoir 404 until the respective ink heights or levels equilibrate. Thus, a supply of liquid ink is always at the ready within the secondary reservoir 404, even as new molten ink is directed into the primary reservoir 402. The supply of ink to be discharged at the printhead assembly is therefore never interrupted, at least as long as the flow of melted ink to the primary reservoir is not interrupted.
In dual reservoir systems of this type, a one-way valve 408 must be interposed into the passageway 406 between the two reservoirs. The valve 408 is operable to permit flow ink from the primary reservoir to the secondary, but not in the opposite direction. The valve 408 is thus closed when the secondary reservoir is pressurized to discharge molten ink to the printhead assembly.
The valve 408 in one typical system is mechanically actuated under power, and under control of the control subsystem 80. Actuated valves of this type are opened and closed in timing with the application and release of pressure to the secondary reservoir. Valves of this type are often costly and occupy significant space within the machine 10.
In another type of system, the valve 408 is a ball valve, which operates passively as a function of the pressure differential between the two reservoirs. When the ink level in the secondary reservoir 404 is low, the pressure differential favors the primary reservoir 402, so the ball valve opens. When the secondary reservoir is pressurized, the differential shifts to favor the secondary reservoir and the fluid pressure pushes the ball valve closed against its seat to prevent ink flowing back into the primary reservoir. Passive ball valves, although generally more economical from a cost and space standpoint, react more slowly than the mechanically actuated valves. The slow reaction times of passive ball valves place a limit on the throughput speed of the storage and control assembly 400, and therefore a limit on the print speed of the machine 10. Moreover, the slow closing rate allows more ink to leak past the ball valve before the seal is made, which in turn leads to a decrease in system performance.
There is therefore a need for a valve system for dual reservoir molten liquid ink systems that is capable of high throughputs, that fits within a limited envelop in the machine and that is cost efficient.